Phase comparison system



July 16, 1957 B. HARRIS (ETAL PHASE COMPARISON SYSTEM Filed April l. 1954 R w w a z l uw l m mm 5 w f ma I n www 0.00 i. .MM/W l mma/47m mim/r: 90

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INI/ENTORS dln.; ai. Mmvrl'l u WORNEY 1 United Staes PHASE coMPArnsoN eterna/i Application April 1, 1954, senat Ne. 420,292

s claims. (C1. str1-sas) The present invention relates to improvements in electrical phase detection and phase comparison circuits, and more particularly, although not necessarily exclusively, to electrical phase comparison circuits of the balanced variety embodying a semiconductor amplifier device connected for a substantially symmetrical type of operation.

More directly, the present invention relates to improvements in electrical phase comparison circuits involving semiconductor amplifier devices of the type disclosed and claimed in a copending United States patent application, by George C. Sziklai, Serial No. 320,712, led November l5, 1952, entitled Phase Comparison, and especially such improvements as lend operating stability and temperature change immunity thereto.

As described in the above-identified Sziklai application, there are many instances, particularly in electrical signaling systems, where there is a need for a phase comparing circuit capable of detecting the sense and magnitude of phase ditierence between two electrical signals. In one common type of phase comparison circuit, a local controllable wave is compared in phase with a standard or fixed reference wave to develop a control signal which may be applied to control the generation of the local wave so as to bring it into synchronous frequency or phase relationship with the standard reference wave. Examples of this type of circuit action may be seen in automatic frequency control systems used for synchronizing the line deflection circuits in television receivers, a commercial embodiment of such a circuit being illustrated in an article by E. L. Clark, entitled Automatic frequency phase control of television sweep circuits in the May 1949 issue of Proceedings of the I. R. E, commencing on page 497.

Phase comparison circ-nits, of course, find many other applications, such as in the automatic frequency control of the local oscillator in a superheterodyne receiver, such that otherwise undesirable shifts in the local oscillator frequency due to line voltage changes, etc., may be avoided.

Prior to the disclosure of the above-identied Sziklai U. S. patent application, a most common form of phase comparison circuit involved the use of two diodes connected in a bridge relation across one source of signal to be compared. The other signal to be compared was in turn fed across the other diagonal of the bridge. The difference in phase between the two signals thus compared was manifested in a change in the average signal current iiow through one branch of the bridge which could be detected and employed for control purposes. Sziklai then contributed to the art by teaching how a bidirectional semiconductor ampliiier could be employed to accomplish with very little circuitry what was theretofore possible through the use of at least two separate diode elements and other circuit complexities. By using a semiconductor amplifier device having substantially symmetrical output and input characteristics whereby the roles of the input and output electrodes in junction relation to a base elecatent f ice trode can be interchanged with no practical change in circuit operating conditions, Sziklai shows that one signal to be compared may be applied to the base electrode of the transistor while the other signal to be compared may be applied across the other two electrodes. Direct current flow between these latter two electrodes is then shown to be a measure of the phase difference between the signals to be compared with the electrical sense of the average current iiow bearing information as to the sense of the phase diierence between the signals.

In the application of the Sziklai semiconductor balanced phase comparator circuit to television receiving circuits, it is expedient to apply received television synchronizing pulses to the semiconductor amplifier base electrode and locally developed deflection signal across the other two electrodes. By capacitively coupling the synchronizing signal to the base electrode, the semiconductor ampliiier may be made to develop its own cutoff bias so that the amplifier is effectively switched or keyed on only during the intervals of the synchronizing pulses. In this way, the developed phase indicating signal results from sampling of the deiiection signal by the synchronizing signal.

Under the conditions where the semiconductor amplifier is subject to wide variations of temperature, circuit operation may be adversely aiected. This comes about by reason of the well known change in the barrier conditions within a semiconductor amplifier as the temperature of the semiconductor material is altered. For example, the terminal impedance between the emitter and collector of a semiconductor amplifier or the comitters of a bidirectional semiconductor amplier during cutoif of the amplier is an inverse function of temperature. As brought out more fully hereinafter, comitters is a term applied to the operating electrodes of a bidirectional semiconductor ampliiier device. This terminal impedance during cutoff is sometimes referred to as the reverse or back impedance of the amplifier. In the above-described Sziklai phase comparator circuit, this back impedance will have a tendency to dissipate some of the error voltage developed by the phase comparator circuit. Since the actual value of the back impedance is a function of temperature, the developed phase comparison error voltage will also undesirably be rendered a function of temperature. Moreover, the back terminal resistance of transistor amplifier operating at a given temperature varies considerably from unit to unit. rIhus, with the basic Sziklai circuit, it is important that care be exercised in replacing the semiconductor amplifier should replacement become necessary.

To improve the temperature stability of this type of phase comparator semiconductor circuit, and to render its operation less critical as to the characteristics of the semiconductor amplifier used, the present invention provides a resistor having a value falling within a narrow range of resistance values and connected between the committers of the bidirectional semiconductor amplifiers described above. In accordance with the present invention, the value of this resistor is made relatively low compared to the lowest reverse impedance value presented by the semiconductor ampliiier (corresponding to the highest operating temperature) while maintaining the value of the resistor suiiiciently high to develop a peak error voltage in response to current flow between the committers large enough to provide adequate frequency control of a wave generator.

It is, therefore, an object of the present invention to provide an improved phase comparison apparatus.

Another object of the present invention is to provide simpliiied apparatus for accurately detecting phase differences between electrical waves applied thereto.

A further object of the present invention is to provide an improved system for indicating the magnitude e 2,799,784 e Y and senses of a phase difference conditionally existing between two electrical signals.

Yet another object of the present invention is to provide an improved phase comparison apparatus embodying a semiconductor amplifier device.

ltisrfurther a general object of the present invention to provide an improvement on the phase comparator circuit disclosed in copending U. S. patent application, Serial No. 320,712., tiled November l5, 1952, by .George C. Sziklai, entitled Phase Comparison,

Still another object of the present invention resides in the provision of a novel semiconductor balanced phase comparator circuit whichjis substantially free from changes in operating characteristics over relativelyy Wide variations, in ambient temperature,

It is yet another object of the present invention to Provide a transistorized automatic frequency. control circuit suitable for use in television Vcathode ray beam deflection circuits inl whichY successful operationV of. the circuit is permitted for a variety o f transistorrunits/ having considerably different operating charactesiicg A more complete understanding of the present invention as well as other advantages and features thereof will be obtained from a reading of the following speciiication, especially when taken in connection with, the accompanying drawings, in which:

Figure 1 is a block and schematic representation of an automatic frequency control systemy embodying the novel features of the present invention.

Figure 2 is a graphical illustration of exemplarly signal relationships which may be encountered in the4 practice of the present invention.

Figure 3 is a combination block and schematicdiagram of a television receiver provided with an automatic frequency control circuit embodying the novel features of' the present'invention for controlling the cathode Vray beam deiiection rate of the receiver.

Turning. now to Figure l, there is illustrated in block form at a source of standard timing signal having a waveform shown at 12. As will become more apparent hereinafter, although the timing signal 12 has been shown as being pulselike in form, the successful practice of the present invention is in no way limited to this particular Wave configuration. The timing signal 124 is conveyed to the control electrode of an amplifier'` 1 4 which, byway of example, has been shown asbeing of the cathode follower variety with an output load resistor 16 connected between the cathode of tubev 14 and circuit ground.Y Stray and/or lumped circuit capacitancewhich may appear across the load resistor V16V is indicated by the dottedlinecapacitor 18. The purpose of the cathode` follower tube 14, as discussed hereinafter, is to ensure a relatively low impedance source of timing signal for the phase comparator circuit to be described. The timing signalas delivered by the cathode follower has been indicatedby the waveform 29. Y Y

Means -such as the capacitor 21 are then provided for coupling the timing signal 20 to the base electrode 22j of,` a semiconductor amplifier 24. rthe semiconductor amplifier 24 which may take the form Vof a symmetrical bidirectional transistor comprises a base electrode 22 and at least two operating electrodes 26 and 28 in cooperativeV relation to the base electrode. By way o'fexample, amplifier 24 may be, of the transistor junction variety in which the operating electrodes 26 and 28 are connected with separate Zones of semiconductor conductivity in junction relation to a base zone to which the base electrode 22 is connected.V For purposes of illustrational convenience, a P-NP type transistor action will be assumed each of the operating electrodes with respectto the baseV is substantially the same whereby either of the operating electrodes may serve as emitter or collector dependingV upon the relative polarity each operating electrode holds with respect to the base electrode. Such a semiconductor amplifier is known in the art as a bidirectional symmetrical unit. Since, in a bidirectional transistor either of the operating electrodes may operate as an emitter or collector, it is appropriate to term the operating electrodes comitters It is in this sense that the term comitters will be used throughout this specification and claims. With this understanding, quotation marks will not be hereafter used presenting this term.

In accordance with thepresent invention, a load resistor 30 is connected between the comitters 26 and 28. The value selected for the resistor 30 and the benefits to be derived therefrom is the heart of the present invention and will be discussed in full, hereinafter.

The signal Whose phase is to beY compared with the standard timing signal is shown by way of example at 32. Although the signal 32, is for purposes of convenience, indicated as being sawtooth in waveform it will be understood that other signal wave forms could be utilized without departing from the spirit and scope of the present invention. The waveform 32 is indicated as being ,developed by sawtooth generator 34 which has a relatively low internal impedance compared to the path impedance Yled or timed by an oscillator 36 whose operating frequency is adapted for control by a frequency control circuit 38. By way of example, the frequency control circuit may be of the conventional reactance tube variety as shown, for instance, on page 655 of theV Radio Engineering Handbook by Terman, first edition 1943. Any error voltage developed across the load resistor 30, which may be indicative of a phase dierenceV between signal 32 and the timing signal 20 is then applied through a lowpass iilter 40 to the frequency control circuit 38.

As is well known in the art, if the error signal developed across the resistor 30 accurately depicts by its polarity and magnitude the sense of, and magnitude, of, the phase difference between the waveform 32 and timing signal 20. The frequency control circuit 38 may be made to maintain a predetermined mode of synchronism between the waveform 32 and the timing signal 20.V

The circuit thus far described in Figure l is substantially the same as that shownY in thev above-referenced United States patent application by George C. Sziklai. Before considering the temperature correction influence provided by assigning a'predetermined value to the load resistor 30, in accordance 'with the Present invention, a general considerationofthe .operation of the Sziklai phase detector circuit will be helpful. As an aid in understandingthe operation lof .FigureV l, reference to the graphrof Figure 2 is desirable. Let it be assumed that it is desirable to maintain the waveform 32 and the timing signalpuises 20 inthe synchronousrelation shown in Figure 2n. The timing signal 2G as'applied Vto the left hand terminal of capacitor 2l will Vtend to charge the capacitor 21 through Y the base of the amplifier 24 with a direction of current indicated by the arrow 44; Thefmaiority of thiscurrent may iow through either Acomitter depending upon the potential relationships of thecomitter torone` anc-ther and the base at the time of the pulse 29. The capacitive-2i. will during the intervals between the pulses 26, be left with the charged condition illustratedV in the ligure, in which the base 22 ofthe amplifier 24 is left positively polarized with respect to circuit ground.` if the amplitude of the timing signal 2@y is made `greater, than the peak to Y peak amplitude of. the waveform 32, itV will follow that transistor type current conduction withinfthe amplifier ,2d Y

cannot occur except during the pulsesll.V Vftransistor aetionV can occur duringgpulses 25 only by virtue of what appears as a forward bias current through the'transi'sto'r amarsi due to the charging of capacitor 21 in the amount corresponding to whatever charge has leaked off during the period between successive pulses. If, during the on period of the amplifier corresponding to the individual pulses 2l), the upper comitter 26 in response to the sawtooth signal 32, tends to swing positively with respect to circuit ground and comitter 28, the comitter 26 will act as an emitter and comitter 28 will act as a collector. This will act to charge the coupling capacitor 35 with its right hand terminal in :a positive potential relation to its left hand terminal. This, of course, will leave the point 46 (or the comitter 26) with an average negative potential with respect to circuit ground. On the contrary, should the instantaneous potential of the right hand terminal of capacitor 35 be negative with respect to circuit ground during the on time of the amplifier 24, the capacitor 35 will tend to charge in an opposite polarity relation, with the comitter 26 acting 'as collector and the comitter 28 acting as emitter. Under such conditions, the average potential of the point 46 (or the comitter 26) will be positive with respect to circuit ground.

Returning now to the consideration of Figure 2a it will be evident that if the timing signal pulses 20 occur during the return or lyback portion 32a of the sawtooth 32 such that the intersection of the AC axis 42 with the return time slope 32a substantially bisects in the pulse 20, the average potential of the point 46 with respect to circuit ground will be substantially zero error voltage will be applied to the frequency control circuit defining the frequency of the oscillator 36. Should the phase of the oscillator 36 shift in a direction corresponding to a decrease in frequency, the waveform relation of Figure 2b will obtain. Under these conditions, it will be seen that the right hand terminal of capacitor 3S will be positive with respect to circuit ground during the on time of the amplifier 24, thereby resulting in a negative error voltage at terminal V46. This may be made to effect a temporary increase in the speed of the oscillator 36 to correct for this phase error. Should the oscillator 36 tend to speed up to produce the phase relation depicted by Figure 2c, a positive error voltage will be developed at terminal 46, thereby tending to slow down the oscillator 36. It is thereby seen that an automatic frequency control type of operation is provided Aby virtue of the basic phase detecting and comparing action of the circuit, involving the semiconductor amplifier device 24.

As brought out in copending United States patent application by Bernard Harris and Albert Macovski, Serial No. 420,240, led April 1, 1954, entitled Phase VComparison System, the finite source impedance of the synchronizing pulses 2@ causes the overall phase comparison circuit to be somewhat unbalanced in operation'. The source impedance of the synchronizing pulses 28 may not only include the resistive component provided by the cathode impedance of the tube 14 in Figure l, but also stray circuitcapacitance indicated by the dotted line capacitor 18. To correct for this, the above-identified Harris et al. U. S. patent application shows that a corrective or balancing impedance may be connected between the ungrounded comitter and base of the semiconductor amplifier as illustrated in Figure l and Figure 3. In Figure 1 a capacitor 48 in series connection with an associated resistor is connected between the comitter 26 and base 22 of the amplifier 24 for this purpose. In Figure 3 capacitor 112 serves the same balancing function. These aspects of the circuit shown in Figures l and 3 forms no part of the present invention and is itself fully claimed in the aboveidentified Harris et al. application.

inV the practical employment of the arrangement in Figure l, consideration must be given to the temperature` responsive characteristics of known semiconductor ampliiiers. lt is common knowledge in the'art that at the present state of development, semiconductor amplifiers of the'transistor variety respond to temperature changes in i 6 a manner so as to decrease the reverse or ofi impedance existing between the operating electrodes such as 26 and 28 in Figure 1 as the ambient operating temperature of the amplifier device is increased. This has been attributed to the change in barrier conditions existing between the operating electrodes at the point where they are connected with the material forming the base element of the amplifier. In the embodiment of the invention shown in Figure 1 this means that if the resistor 3G forming the load between the comitters 26 and 28 of the bidirectional semiconductor amplifier 24 is made very high in value, the amount that the capacitor 35 will discharge between successive peaks of the sawtooth signal 32 will be a function of the reverse impedance between the comitters 26 and 28. This reverse impedance, of course, is of interest only during the off time of the amplifier 24, which corresponds to the interval between successive synchronizing pulses 20 as described above. If the value of the resistor 30 is made too low, insufficient voltage will be developed across the resistor in response to current iiow between the comitters 26 and 28 to deliver a peak correction voltage to the filter 40 of sufficient magnitude to eectively operate the frequency control unit 38. In practice, it is found that 1most frequency control units (such as the well known reactance tube circuit) requires from three to ve volts of control signal to produce a suicient change in its operating characteristic to in turn adequately control the frequency of the oscillator or signal generator designated for control thereby.

In television deection circuits, such as will be considered in the discussion of Figure 3, the magnitude of voltage delivered to the frequency control unit is a direct indicia of the pull-in range and speed of action of the overall automatic frequency control circuit. Thus, in accordance with the present invention, the value of resistor 30 is determined in terms of the duty cycle of the signal pulses 20, the voltage required across the resistor for AFC purposes and the desired peak current operating condition 0f the semiconductor ampliiier 24. Where the duty cycle of the pulses 20 may be expressed as D, the peak current to be passed by the transistor 24 in response to forward base current (representing the charging of capacitor 21 by the pulses 20) represented by ip, and the voltage it is desired to deliver to the filter network 40 is represented by V, the value R of resistor 30 should be, in accordance with the present invention, no less than Dip.

The duty cycle D is to be expressed as the fraction of the whole repetition period of the signal pulses 20 which the amplifier 24 is actually rendered conducting. In instances where the back resistance between the comitters 26 and 28 is substantially higher, for example by a factor of three to ve times the selected value of the resistor 30, temperature variations will not greatly affect the developed value of the control voltage applied to the filter network 40. In general, however, it is desirable to make the resistor 30 as low as possible consistent with the development of adequate AFC potential in response to the peak current capabilities of the amplifier 24.

By establishing the value of the load resistor 30, in accordance with the above teachings of the present invention, it has been found that relatively wide variations in ambient operating temperature can be tolerated by the circuit shown in Figure 1 (such as 30 F. to 130 F.) without excessively impairing the efficacy of circuit operation.

The embodiment of the present invention shown in Figure 3 is substantially the same as that shown in Figure 1, with the exception that the automatic frequency control circuit is shown in operating connection with the horizontal deection circuit of a television receiver. Moreover, the polarity of the sawtooth signal employed in Figure 3 is opposite to that employed in Figure 1.

l,In Figure 3 a television receiver tuner 50 is ,shown adapted to receive radio signals from anantenna 5,2. Output signal ffrom the tuner 50 is appliedin Ya conventional manner to an intermediate frequency amplifier 54 which is in turn Ycoupled to a signal demodulator 56. A video amplifier S is then fed by `demodulated video signal provided by the demodulator 56.' Output signal from the video amplifier 58 is applied to the kinescope 60 for modulation of the cathode ray beam therein. The demodulated video signal is also extracted from the video amplifier 58 and applied to a conventional form of sync separator circuit 62. Separated sync 6'4 is then applied to the control electrode 6,5V of a sync amplifier tube 68, whose anode 70 is connected through a load resistor 72 to a source of anode supply potential h aving a positive rterminal at 74. The negative terminal' of the anode supply source is shown grounded at 762 'Negative going separated and amplified synchronizingv signal 78" is capacitivelyV coupled' via the capacitor 80 to the base electrode 82 of a semiconductor type amplifier S4. The amplifier 84' is shown, purely by way of example, as being of the same general type as the amplifier 24 in Figure 1. A sawtooth deflection signalfor comparing with. the incoming sync may be conveniently derived fromrtheY output circuit of a horizontal deflection amplier 3S. To illustrate this a capacitor 90' isY shown connected' from one terminal of the horizontal deection coil winding within the deflection yoke 92 to the comitter 94 of the amplier V84. Sawtooth signal illustrated by the waveform 98 may be seen to be ofA an opposite polarity Vto that shown at 32 in Figure 1.

`In the arrangementl of Figure 3', in contradistinction to the circuitry of Figure 1, the comitter 100 of vFigure 3 is connected with circuit ground through a Vtime constant load circuit 102- comprising the capacitor4 104 and resistor 106. The position of the circuit 102 appliesa somewhat stabilized bias voltage to the comitterl-Gand at the same time permits the'developed bias Yto be used asV aV control voltage for the reactance tube circuit indicated at 108. T hereactance tube108'isin turn coupled with a horizontal deflection-oscillator 110, which in a conventional'manner, is directed togdrive the horizontal `deflection amplifier 88. An analysis of' theY circuit of Figure 3v will reveal that the sense of the correction voltage developed acrossthe time constantY network 102eis the same as that developedatpoint 46 for a given phase difference between the sawtooth signal 98 and the separated synchronizing signal 78, even though the sawtooth signal 93: is of opposite polarity to that used in Figure 1. As described above, the balancing capacitor 112 may be made to compensate for the finite source impedance of the synchronizing signal 78.

:To achieve the,V temperature compensation effect of-the present invention, in Ythe arrangement of Figure 3, the value of resistor 106 is determined in accordance with the above considerations given in valuing Vresistor 30, illus# trated in the embodiment of the invention Yshown in Figure l.

Resistor 9S is connected from the comitter94 to circuit ground to Vform .pa ilow impedance source of the sawtooth signal V98. Inrpractice, the resistor 95 is made no greaterV than a few ohms so that itsvvalue may beV considered negligible compared to the value determined for resistor 106,V although actually forming a part of the load circuit between comitters andli. Assuming a standard type t of television signahsuchas is usedlin the United States, isbeingreeeived by the arrangement of FigureS, the duty cycle of Vthe synchronizing pulses, having a vrecurrence Y requency of 15,47501C. P; S, is about 1/0Y ofthe recurrence period of these pulses. With/anfassumed'peak current capacity for the semiconductor amplifier S4 of, for example, vemilliamperes and adesired AFC voltage of Yve volts, the value of resistor 105 would in accordancerwith the criteria of the presentinventionfset forthabove Vbe deter- VYminedfat 20,000 ohms.Y Thesemiconductor'amplier S4 upon bvllgheated'from 30 F. to 13001?. might display a change in back resistancey between, the, ,comitters 9 ,4y and 100 from one megohm down to 50,000, ohms. Withthe,

resistor 106 valued at 20,000 ohms it can be seen that for normal temperature variations as mightbe encounteredl in home instrument television receivers, the voltagey de- Purely by way of illustration, and with no intention of limiting the practice and scope of the present invention,

the .following exemplary circuit values are given for the .embodiments of the present invention shown in Figures 1 and 3. Although the circuit values to be given have been found to give good results in the practical application of`V the present invention, to home type television receiving equipment it will be understood that other circuit values,

falling within the scope of the present invention,V asV described hereinabove and yclaimed more fully hereinafter,

may be used with equally satisfactory results: l

For convenience, condensers willbe designated' as C and resistors by R, each followed by the index number assigned to such elements in the drawing.

IN FIGURE l Amplifier 24.-A transistor type TA-211, selected for maximum symmetry C22, and` C48 init 1,80Y C35 uf .05 R30 ohms 20,000 R47 do 100,000

IN FIGURE 3 Amplifier 84.-A transistor type Tf1-211, selected for maximum symmetry C andv C112 uf .0l R72 ohms 50,000 R114 dn 20,000 R95 d0 10,000 C uf .05 C104 ,uf .05' R106 being cooperatively associated with said base electrode,` Vsaid semiconductor amplifier having temperature response characteristics such that a cutoff output impedance is expressed between said operating electrodes during conditional periods of'amplitier cutoff which is an inverse function of ambientoperating temperature kover a desired predetermined temperature range; a rst capacitor connected between one terminal of said first signal sourcev and said base electrode; a connection fromithe other terminal of said first signal source and said first operating electrode such that said first capacitor is charged by said rst source of signals through forward input current to said base electrode thereby tending to produce transistor type conduction between said operating electrodes during said charging intervals, the magnitude of said signals from said iirstsource, and the value of said capacitance means being adjusted to produce a net potential on said capacitance means of a value producing cutoff of saidV amplier during periods between said charging intervals; a connection from said first operating electrode and one terminal of said second signal sourcegra second capacitor con-VVV nected from the other terminal of said second signal source to said second operating electrode such as to conditionally chargesaidsecond capacitor from said second Y nhms l20,000Y

signal source to a predetermined voltage value upon an on conduction condition between said operating eleotrodesv and resistance means connected between said rst and second operating electrodes for developing an output signal indicative of the phase relation between said first and second signals, the value of said resistance means being substantially less than the lowest cutoff output impedance expressed between said operating electrodes over said desired predetermined temperature range.

2. In an electrical phase comparator circuit conditionally subject to wide ranges in ambient operating temperatures, the combination of: a rst two terminal source of periodic electrical signals having a relatively low output impedance value; a second two terminal source of electrical signals whose phase relative to signals from said first source is to be compared; a semiconductor amplifier having a base electrode, a tirst operating electrode and a second operating electrode, said operating electrodes being cooperatively associated with said base electrode, said semiconductor amplier having temperature response characteristics such that a cutoff output impedance is expressed between said operating electrodes during conditional periods of amplifier cutoff which is an inverse function of ambient operating temperature; a rst capacitor connected between one terminal of said first signal source and said base electrode; a connection from the other terminal of said rst signal source and said rst operating electrode such that said first capacitor is charged by said first source of signals through forward input current to said base electrode thereby tending to produce transistor type conduction between said operating electrodes during said charging intervals, the magnitude of said signals from said first source and the value of said capacitance means being adjusted to produce a net potential on said capacitance means of a value producing cutoff of said amplier during periods between said charging intervals; a connection from said rst operating electrode and one terminal of said second signal source; a second capacitor connected from the other terminal of said second signal source to said second operating electrode such as to conditionally charge said second capacitor from said second signal source to a predetermined voltage value upon an on conduction condition between said operating electrodes; and resistance means connected between said iirst and second operating electrodes for developing an output signal indicative of the phase relation between said first and second signals, the value R of said resistance means is no less than the value substantially defined as follows:

Dip

where V is the maximum predetermined voltage value to which it is desired to charge said second capacitor, ip is the maximum peak current to be passed between said first and second operating electrodes and D is the fraction of the period of said rst electrical signal during which said ampliier is rendered conductive by said first electrical signals.

3. In an electrical phase comparator circuit conditionally subject to wide ranges in ambient operating temperatures, the combination of: a lirst two terminal source of periodic electrical signals having a relatively low output impedance value; a second two terminal source of electrical signals whose phase relative to signals from said tirst source is to be compared; a semiconductor amplifier having a base electrode, a first operating electrode and a second operating electrode, said operating electrodes being cooperatively associated with said base electrode, said semiconductor amplifier having temperature response characteristics such that a cutoi output impedance is expressed between said operating electrodes during conditional periods of ampliiier cutoff which is an inverse function of ambient operating temperature; a first capacitor connected between one terminal of said first signal source and said base electrode; a connection from the other terminal of said first signal source and said first operating electrode -such that said first capacitor is charged by said first source of signals through forward input current to said base electrode thereby tending to produce transistor type conduction between said operating electrodes during said charging intervals, the magnitude of said signals from said first source and the Value of said capacitance means being adjusted to produce a net potential on said capacitance means of a value producing cutoff of said amplifier during periods between said charging intervals; a connection from said first operating electrode and one terminal of said second signal source; a second capacitor connected from the other terminal of said second signal source to said second operating electrode such as to conditionally charge said second capacitor from said second signal source to a predetermined voltage value upon an on conduction condition between said operating electrodes; and resistance means connected between said first and second operating electrodes for developing an output signal indicative of the phase relation between said first and second signals, the value of said resistance means being substantially less than the'lowest value of cuto output impedance expressed between said operating electrodes but no less than the value substantially defined as follows:

where V is the maximum predetermined voltage value to which it is desired to charge said second capacitor, ip is the maximum peak current to be passed between said first and second 'operating electrodes and D is the traction of the period of said irst electrical signal during which said amplifier is rendered conductive by said irst electrical signals.

4. In a keyed semiconductor amplifier circuit conditionally subject to wide variations in ambient operating temperatures, the combination of a semiconductor amplifier having a base electrode and a first and a second operating electrodes cooperatively associated with said base, said semiconductor amplifier having temperature response characteristics such that a cutoff output impedance is expressed between said operating electrodes during conditional periods of amplifier cutoi which is a function of ambient operating temperature; means including a first source of periodically recurrent keying signals connected between said base and said first operating electrode for periodically keying the mode of said amplifier between a cutoi condition and an operative condition; a second source of periodically recurrent electrode signals; means including the serial connection of a capacitor coupling said second source of signals between said amplifier first and second operating electrodes so as to conditionally charge said capacitor from said second signal source upon being keyed into an operative condition by said keying signals it being desired to charge said capacitor to a predetermined voltage value; and a resistor connected between said first and second operating electrodes, the value R of said resistor being no less than the value substantially delined as follows:

where V is the maximum predetermined voltage value to which it is desired to charge said second capacitor, ip is the maximum peak current to be passed between said first and second operating electrodes and D is the fraction of the period of said first electrical signal during which said amplifier is rendered conductive by said first electrical signals.

5. In a keyed semiconductor amplier circuit conditionally subject to wide variations in ambient operating temperatures, the combination of: a semiconductor amplitier having a base electrode and a rst and a second operating electrodes cooperatively associated with said base,

ditional Vperiodsof amplifler'rcutol which is a function of ambient operating temperature; means including a first` source of periodically recurrent'keying signals connected between saidV base and said first operating electrode` for periodically keying the mode ofsaid amplifier between a cutoff condition and an operative condition; a second source of periodically recurrentV electrical signals; means including the serial connectionof a capacitor coupling said second source of signals between said ampliiier rst andv second operating electrodes so as Yto conditionally charge said capacitor from saidrsercond signal source upon being keyed into an operativeV condition by said' keying signals it being desiredeto charge said capacitor 'to a predetermined voltage value; and aA resistor connected between saidirst and second operating electrodes, the value of saidrlr'esistance means beingrsubstantially lessV than the lowest value'of cutoffV output impedance expressed between said` operating electrodes but no less than the value substantially deiined4 as follows:

WherejVV is the. maximum towhichgit is desired to chargev saidsecond capacitor, ip

is the maximumy peak current to be passed between said Y first and second operating electrodes and D is the fraci tion,` of the period of said first electrical signal during which said amplifier is. rendered conductiveby saidirst;

electrical signals.

ReferencesgCited inthe le of thispatent UNITED STATES PATENTS Eberhard Dec. 5, 1,950 Gehman .uly`,`7Y 1953 OTHER REFERENCES 20 et al. (Copy in Patent Oce Library.)

predeterminedY voltage; value 

